This invention relates to pressure-sensitive adhesive labels and decals, and particularly to the manufacture of same using radiation-cured films.
For a long time a customary process of manufacturing pressure-sensitive adhesive labels has involved production of a sheet or roll of laminated construction comprising a layer of label feedstock, a layer of a pressure-sensitive ("P/S") adhesive, and temporary carrier having a release surface. More specifically, a carrier web having a release surface, e.g., a plastic film or a smooth paper having a release layer of silicone, is engaged with a web of a label feed stock having a pressure-sensitive adhesive, with the pressure-sensitive adhesive being in contact with the release surface of the carrier web. The face stock may be made of paper or a suitable synthetic material such as a vinyl plastic material, and the face stock may be blank or may have printed indicia. Discrete labels are formed on the carrier web by die-cutting through the label face stock and the adhesive layer without perforating the carrier web. A standard practice is to make the laid-on labels using a die-cutting procedure as disclosed in the following U.S. Pat. Nos.: 4,253,899; 4,219,596; 2,391,539 and 3,166,186. Such labels are commonly referred to as "laid-on labels". Subsequently the face stock and the adhesive surrounding the individual labels are stripped as a continuous skeletal web or matrix, leaving discrete spaced apart labels adhered to the carrier web. The laid-on labels are then dispensed from the carrier web either manually or by a suitable automatic procedure.
The foregoing standard manufacturing technique suffers from the disadvantage of the need to die-cut the label face stock. This die-cutting procedure is expensive due to wasted face stock material and the need for precision die-cutting machinery.
Laid-on labels also may be made without die-cutting as disclosed in U.S. Pat. No. 4,022,926, issued to A. K. Keough et al for "Label Assemblies Without Die-Cutting". However, this form of label manufacture has limitations due to (1) the occurrence of beads of the label face film between adjacent labels, which constitutes non-adherent waste and may adversely affect equipment performance, and (2) the relative stiffness of the face film/adhesive laminate limits the ability to reliably dispense the labels and apply them to the desired workpiece, e.g., bottles. Also, the method of the patent commences with the step of applying a P/S adhesive to a temporary carrier web, and then printing the face film onto the adhesive. This order of steps presents the possibility of damaging the adhesive when the face film is printed.
A different approach was proposed in U.S. Pat. Nos. 4,253,899 and 4,219,596, both issued to Shiro G. Takemoto et al. These patents propose a method of making matrix-free labels. The label construction proposed by Takemoto et al comprises the following:
(1) a temporary carrier having a release surface; and
(2) a label releasably adhered to the release surface of the carrier, with the label taking the form of a face film in contact with the release surface and a layer of pressure-sensitive adhesive on the side of the face film opposite the carrier, with the layer of pressure-sensitive adhesive being substantially in registration with the face film. In one embodiment Takemoto et al also provide a protective backing having a release surface in contact with the adhesive layer, the adhesion between the adhesive and the release surface of the protective backing being weaker than the adhesion between the face film and the release surface of the carrier, so as to enable the protective backing to be removed from the label and thereby expose the layer of adhesive while leaving the label releasably adhered to the carrier. In this label construction, the face film comprises a radiation-cured polymer.
The label construction of Takemoto et al is manufactured by a process that preferably involves the following steps:
(1) forming discrete label face films on the release surface of the carrier web by coating discrete areas of the release surface corresponding in size and configuration to the labels being formed with at least one layer of a radiation-curable liquid;
(2) curing the aforesaid liquid by exposure to polymerizing radiation;
(3) applying a pressure-sensitive adhesive in liquid form over the discrete liquid face films so that the adhesive is substantially in registration with the label face films; and
(4) solidifying the liquid adhesive so as to form discrete labels, with each label having a face film releasably adhered to the release surface of the carrier web and a layer of pressure-sensitive adhesive on the side of the label facing away from the carrier web. If a protective backing sheet is used, it is applied after the pressure-sensitive adhesive layer is formed, with the adhesion between the adhesive and the release surface of the backing being weaker than the adhesion between the face film and the release surface of the carrier web, so that the protective backing may be removed from the label to expose the layer of adhesive on the label while leaving the label releasably adhered to the carrier web.
The technique disclosed in U.S. Pat. Nos. 4,219,596 and 4,253,899 avoids the die-cutting operation, and also the resulting loss of face stock. However, the method of making labels and decals disclosed in U.S. Pat. Nos. 4,219,596, and 4,253,899 has the disadvantage that it requires substantially exact registration of the pressure-sensitive adhesive with the discrete label face films. This is a disadvantage in that substantial precision is required to obtain the degree of registration required by Takemoto et al, since if the adhesive does not fully cover the face film, the edges of the face film will not adhere to the surface of the object or workpiece to which the label is transferred.
A related method of making labels is disclosed in British Patent Specification No. 827,313, published Feb. 3, 1960. This patent discloses a dry-release pressure-sensitive label construction comprising a printed layer or assembly of layers which are adapted to be transferred and are printed or coated on a temporary dry-releasing paper support from which the printed layer or layers may be dry-released, with the paper support being impregnated or coated so as to have a release surface. The method and label construction disclosed in British Patent Specification No. 827,313 provides teachings similar to those of Takemoto et al but is handicapped in that it does not utilize radiation-curable polymers to form the labels. Reed uses a solvent based system that is eminently unsatisfactory because of disposal concerns and also because it is limited as to printing speed.
Reed also does not address the question of registration of the several layers of his label construction, particularly as it affects the reliability of the adhesion of the label to the support to which it is ultimately transferred.